Abstract
Salt-affected soils have poor structure and physicochemical properties, which affect soil nitrogen cycling process closely related to the environment, such as denitrification and ammonia volatilization. Biochar and polyacrylamide (PAM) have been widely used as soil amendments to improve soil physicochemical properties. However, how they affect denitrification and ammonia volatilization in saline soils is unclear. In this study, the denitrification and ammonia volatilization rates were measured in a saline soil field ameliorated with three biochar application rates (0%, 2%, and 5%, w/w) and three PAM application rates (0‰, 0.4‰, and 1‰, w/w) over 3 years. The results showed that denitrification rates decreased by 23.63-39.60% with biochar application, whereas ammonia volatilization rates increased by 9.82-25.58%. The denitrification and ammonia volatilization rates decreased by 9.87-29.08% and 11.39-19.42%, respectively, following PAM addition. However, there was no significant synergistic effect of biochar and PAM amendments on the denitrification and ammonia volatilization rates. The addition of biochar mainly reduced the denitrification rate by regulating the dissolved oxygen and electrical conductivity of overlying water and absorbing soil nitrate nitrogen. Meanwhile, biochar application increased pH and stimulated the transfer of NH4+-N from soil to overlying water, thus increasing NH3 volatilization rates. Hence, there was a tradeoff between denitrification and NH3 volatilization in the saline soils induced by biochar application. PAM reduced the denitrification rate by increasing the infiltration inorganic nitrogen and slowing the conversion of ammonium to nitrate. Moreover, PAM reduced the concentration of NH4+-N in the overlying water through absorbing soil ammonium and inhibiting urea hydrolysis, thereby decreasing NH3 volatilization rate.
Highlights
Soil reclamation plays a crucial role in coastal development in China
There was a tradeoff between denitrification and NH3 volatilization in the saline soils induced by biochar application
PAM reduced the concentration of NH4+-N in the overlying water through absorbing soil ammonium and inhibiting urea hydrolysis, thereby decreasing NH3 volatilization rate
Summary
Soil reclamation plays a crucial role in coastal development in China. From 1985 to 2016, a total of 9 310.6 km of tidal flats were reclaimed in the eastern coastal areas of China, and farmland accounts for 41% of the reclaimed area (Liu & Li 2020). NH3 volatilization cause a series of ecological and environmental problems, such as air pollution, acid rain formation and eutrophication in water (Schiermeier 2013; Zhu & Chen 2002) Both denitrification and NH3 volatilization processes are affected by many factors, including the physical and chemical properties of water and soil, such as nitrogen concentration, pH, salinity and dissolved oxygen (She et al 2018; Vega-Jarquin et al 2003). It is imperative to understand the underlying mechanism of N losses through denitrification and NH3 volatilization and increase the N utilization efficiency in coastal saline soils from both the sustainable production and the environmental viewpoints
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